svxcalibur,

My son did a similar thing to his '94 - used low octane gas - and it caused the same systems to describe. What worked for us was, we ran it till it was almost out of gas, then refilled with premium and STP gas treatment…. We did this twice. The car started and ran much better. Then we disconnected the battery for about 24 hours (to clear the codes - see archived posts)…. And the check light hasn’t come back on since…

Good luck..